Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$100.92	10.570%	$111.5872	$111.59	$111.60	$111.60
Purchase #2	$246.85	12.418%	$277.5038	$277.50	$277.50	$277.50
Purchase #3	$100.57	3.671%	$104.2619	$104.26	$104.25	$104.30
Purchase #4	$53.37	6.511%	$56.8449	$56.84	$56.85	$56.80
Purchase #5	$146.30	3.136%	$150.888	$150.89	$150.90	$150.90
Purchase #6	$104.87	12.332%	$117.8026	$117.80	$117.80	$117.80
Purchase #7	$197.31	12.799%	$222.5637	$222.56	$222.55	$222.60
7 purchase totals =	$950.19		$1,041.4521	$1,041.44	$1,041.45	$1,041.50